Effects of landscape factors, precipitation and individual plants on nitrogen mineralization (LT19)
(ARS #42)
Paul B. Hook
Indy Burke, Dept of Forest, Range, and Watershed Stewardship, Colorado State University, Ft. Collins, Co 80523
970-491-1620 indy@cnr.colostate.edu
Objective: Evaluate spatial and temporal variability of growing season N mineralization in relation to (1) the landscape factors, soil texture, and topographic position (upland and lowland areas that are predominantly erosional vs. depositional areas), (2) microsites under Bouteloua gracilis plants and in natural interspaces, and (3) month-to-month variation in rainfall. Each of these factors has been hypothesized to be an important control of N dynamics and availability; we will try to compare their relative influences and evaluate interactions.
Methods: Design: 10 Locations: 10 paired uplands and lowlands selected to include a wide range of textures in both positions; 5 will have upland soils developed in sandy loam eolian material and 5 will have upland soils developed in shale. The latter are located in areas mapped as Renohill-Shingle complex by the SCS. 2 Topographic positions: upland and lowland plot at each location for a total of 20 plots about 10 X 10m. 2 Microsites: under and between plants. 4 Dates: Monthly sampling of soil cores and resin bags (Install late June, collect in July, August, September, and October). 2 Duplicate samples for each microsite X topographic position X location combination. Total of 400 soil cores (including initial sample) and 320 resin bags; 20 cores in 20 plots. Methods: (1) in situ incubations to estimate N mineralization. 5cm diameter X 15cm deep soil cores with ion exchange resins at base. All soil will be replaced with sand, or with local soil of same texture if desired. These samples will also be used to estimate other soil properties to minimize soil removal. (2) ion exchange resin bags to estimate patterns of N availability. 5 X 2cm nylon bags with exchange resins buried below 5cm depth. These will be inserted in small slits in soil made with a trowel and will be placed and collected monthly. (3) soil water monitoring by time domain reflectometry. TDR probes (2mm diameter stainless stell rods extending about 1cm above soil) will be placed in and adjacent to each core. These are non-destructive and will be removed as cores are collected. Rainfall will be colleted at several sites. We do not anticipate need to exclude cattle in any way; if disruption by cattle appears to be a problem, use of a small number of 1m cages at each plot may be requested.
Study Area: We re requesting low intensity use of paired upland and lowland plots at 10 locations across the CPER: Pastures 15SW (SW 1/4), 19 NW (SW corner), 22NW (NW 1/4), 21NE (SE 1/4), 25SE (E1/2), 26NE (SW 1/4), 26SW (NW 1/), 27NW (NW 1/4), 28NE (NE 1/4), 19NE (NE 1/4); map attached. Each pair of plots will be separated by 50-150m. Each plot will be about 10 X 10m as need to include required microsites; plots will not be fenced and 40 small soil cores per plot will be collected over 5 months. All locations are in moderately grazed pastures. Locations have been selected to meet the design criteria outlined below, but other locations may be suitable and we are ready to select other locations if necessary to avoid conflicts with other research. Several locations were chosen specifically for poximity to current or previous research: e.g. 21N, 25SE, 26SW, 26NE. We have discussed potentially complementary or conflicting work at these locations with D. Coffin and D. Valentine.
03/21/2002